This invention relates to electron beam deflection devices and more particularly to electron beam deflection amplifiers.
Electron beam deflection type tubes are well known devices used to provide RF signal amplification. For good reproduction of amplified signals, such amplifiers must be designed to provide excellent sensitivity characteristics. Such characteristics assure that small variations of beam deflection produce corresponding large variations in output current thereby enhancing the usefulness of such devices as high-gain RF amplifiers. Heretofore, electron beam deflection amplifiers generally utilized a single electron beam wherein the amplified output signal is a function of the beam deflections resulting from the input signal. One of the problems experienced in the operation of such sensitive, single electron beam deflection amplifiers is the effect of stray magnetic fields external to the device. Such fields arise from the earth's magnetic field, from steel and other magnetic materials, from power transformers and other equipment components proximate to the amplifier. With static fields, this is equivalent to a stray deflection bias. Variable fields emanating from power equipment and power line transformers cause stray modulation of the electron beam, which, in turn, causes extraneous modulation of the output amplified signal. In highly sensitive beam devices such as those utilizing electron bombarded semiconductor (EBS) target elements, for example, these stray external fields are very detrimental to the operation of the amplifier and may even destroy its usefulness. While such tubes may, to a certain extent, be provided with external shielding means, such shielding is highly undesirable since it is rather cumbersome, requires a great deal of space and adds unwanted weight. Also, at high voltages the metallic shielding material may cause arc-overs or unwanted corona effects.